The invention relates to friction welding machines particularly machines having means for removing "flash" from the weld zone.
Friction welding machines having flash removal means are known but the problem of flash removal is not satisfactorily overcome by the known proposals. In particular, friction welding machines intended for use in high volume production work of high standard must grip both workpieces very close to the ends of the workpieces which are engaged during welding. Also, the mechanical construction of the machine must be kept simple so as to minimise the risk of malfunction of the machine in the production environment.
In one type of known machine (see for example U.K Pat. application Nos. 1,182,111 and 1,323,678), the flash is removed by a tool permanently secured to one of the workpiece holders. A backstop, which supported one of the workpieces against the high load applied during welding, must be displaced before the flash is removed in such machines.
This is unsatisfactory because:
i. the presence of the tool prevents one workpiece from being gripped sufficiently close to the weld face. PA0 Ii. the backstop mechanism which permits the backstop to be displaced is not practicable because it must be designed such as to be able to support very high loads and yet be releasable and displaceable in a simple and rapid manner. No such mechanism has to date been incorporated in machines used in high volume production. PA0 Iii. the tool cannot be readily re-ground and re-grinding holds up production. PA0 Iv. the presence of the tool permanently in the working space between the two workpiece holders makes the introduction and removal of workpieces difficult and further reduces production efficiency.
In a similar type of machine (see U.K. specification No. 1,323,812), the tool is permanently secured to one workpiece holder but instead of displacement of a backstop, the tool is positioned on the remote side of the weld zone from the workpiece holder to which it is attached. This requires that the tool be secured to the holder by a relatively long member and the considerable loads imposed on the tool during shearing of flash are clearly not adequately resisted by such an arrangement since the tool is not properly supported. The working space and access to it are both severely restricted.
In another type of machine flash is removed by a tool permanently mounted on a workpiece holder which is rotated about the weld zone (see U.K. specification No. 1,392,581) but this requires considerable complication in the construction of the workpiece holder on which the tool is mounted. The workpiece is gripped too far away from its weld face and the working space and access to it are severely restricted.
In another type of machine, flash is removed by a tool which cuts the flash as it is rotated relatively to the tool (see U.K. Specification No. 1,309,043).
In such a machine the removal of the flash produces swarf of a kind which is difficult to handle and which includes particulate swarf which cannot be removed from the working space and the machine eventually has to be stopped to enable the swarf to be cleared away. Obviously, this is totally unsuited to high volume production work. Furthermore, the method is relatively slow.
Another machine (see U.K. Specifications Nos. 1,304,933 and 1,304,413) purports to remove flash as it is formed but in fact this is extremely difficult to achieve in practice, if not impossible. There is no tool material which will withstand the combination of very high temperatures and repeated high loading which this procedure imposes on the tool and the method is not available for adoption in production work.